water pump 300 sel 4.5 - PeachParts Mercedes-Benz Forum

tosbt · #1 12-25-2003, 09:24 AM

Why did my new water pump fail? Less than 800 miles and it started to leak yesterday. About 3/4 inch flex on belts. Did hit 115 mph last ride. Merry Christmas!

Tomguy · #2 12-25-2003, 11:50 AM

I assume you're saying that the .75" flex is not overtightening the belts - unless it could be due to play in the shaft. I have gone well over 135 on several occasions and my water pump is original, so I doubt that's why

Could it be a bad seal, or is it a defective pump? It is possible (though not common) to get a bad pump. When you sealed it, did you put any silicone RTV sealant on the gasket? I've done 2 water pumps - '86 Nissan P/U w/Z24 (w/140K at time, 160K miles brought head gasket failure but wouldn't pass inspection due to body rot after I fixed it..) and '92 Jeep Cherokee 4.0L w/130K at time, neither leaked on me, and I put blue Permatex on the gaskets of both (and let it "cure" for 10 mins before installing it) and neither leaked. The instructions for the Nissan one didn't say to do it but the ones for the Jeep did (I did the Nissan one about 1yr before the Jeep one).

jim16671836 · #3 12-25-2003, 01:18 PM

Double check to make sure it is not the gasket..and you have been using antifreeze.????

Clunker · #4 12-25-2003, 01:56 PM

tosbt, Welcome to Hell! I can't tell you why it failed but If you have never changed a 300sel 4.5 before it's a job! You have to pull the distributor and reset the timing: a great time to do a bunch of things while you are at it: belts, hoses. fluids, radiator flush, points, etc. Do not use a cheap water pump!! I cannot stress that enough. I've done it. I've played the chump before, never again. What type of pump was it replaced with 800 miles ago?

300SDog · #5 12-25-2003, 06:25 PM

Sounds like bad luck with aftermarket parts that could have been sittin on the shelf for 30 yrs.... leakin through weep holes on the pump itself?

Workin with what Jim asked about anti-freeze - MB dealership will recommend their own coolant that has water pump lubricant in it. But DIY'ers have discovered that Prestone Orange formula has the same stuff with the same specs for lubrication - much better than ordinary green anti-freeze.

Last edited by 300SDog; 12-25-2003 at 06:38 PM.

WANT '71 280SEL · #6 12-26-2003, 01:00 AM

DO NOT use orange dex-cool. I work for a used dealerships and the stuff turns to mud fter two years. It is suppose to last 5yrs/150k miles, my a**. It turns dark brown and you will notice it coating everything in your cooling system. I don't know if it loses it's cooling properties/lubrication properties, but I do know what it looks like after a couple years. I talked to a guy in the service dept. at the MB dealership here and he said to just use regular green coolant in my friend's 280SEL 4.5. He said that about 7-8 years ago something happened to MB coolant or to green stuff that it is about the same now. My point is, use the crap coolant in the crap cars.
David

Tomguy · #7 12-26-2003, 01:26 PM

David: That's often the result from reactions with acids (the coolant neutralizes acids but unfortunatley, doesn't always do it well when there's a lot of it). I've seen it happen with the green stuff too. But I've seen worse with the green than the red - the deposits, the rust, the galvanic action, etc!
I don't think the green stuff is that bad - hell, I use it in my Jeep. But if the guys here (whom I consider to be experts) tell me to use the red in my MB, I'll use it!

#8 12-26-2003, 05:17 PM

He is saying to use green, just don't use the red.
Tim